Tag: extinction

The healthy little brown bats roosting close to the bat
with white-nose syndrome risk infection with the fungus

The deadly fungus that causes white-nose syndrome is sweeping through North American bat populations, and little brown bats are adapting their behavior to avoid it. Although these bats typically clump together in large groups, they are now spreading out to roost separately, a change in behavior that may be helping the bat populations rebound. So what does a bat-killing fungus have to do with human prejudice? The bats’ trick of splitting up to survive contagion may also have led humans to divide into tribes and respond hostilely to members of different, potentially diseased groups.

In a post on Scientific American’s Guest Blog, biologist Rob Dunn writes about the link between infectious diseases and human prejudice.

Nature changes gradually—until it doesn’t. As the changes in an ecosystem pile up, they can push the system past a “critical threshold,” and then the change can become extremely fast (in relation to geological timescales) and unstoppable. And in a review in the journal Nature, researchers suggest that the same thing is happening to the whole world: Humans could be driving Earth’s biosphere towards a tipping point beyond which the planet’s ecosystems will collapse abruptly and irreversibly.

This global ecosystem collapse has occurred before, most recently about 12,000 years ago with the last transition from a glacial period to the current interglacial (i.e., warm) period, say the review authors. Over the relatively short period of 1,000 years, fluctuations in the Earth’s climate largely killed off about half the large mammal species, along with birds, reptiles, and a few smaller mammal species. The millennium-long shift was triggered by rapid global warming, and once this warming pushed the planet past its tipping point, the end of the 100,000-year-old ice age became inevitable, giving way to the current 11,000-year-old interglacial era.

What’s the News: The loss of large animals is wreaking havoc on Earth’s ecosystems, according to a scientific review published in Science on Friday, causing food chains to fall into disarray, clearing the way for invasive species, and even triggering the transmission of infectious diseases. The decline and disappearance of these large animals, due in large part to human factors such as hunting and habitat loss, has such strong and wide-ranging effects that the review’s authors say it may well be “humankind’s most pervasive influence on nature.”

What’s the News: Researchers have uncovered the youngest known dinosaur bone, dating from shortly before an asteroid slammed into Mexico’s Yucatan peninsula around 65 million years ago. The find, published today in Biology Letters, has revived debate among paleontologists over what, exactly, killed the dinosaurs.

What’s the News: A fungus that his been wiping out frog species all over the world is creeping into the last area patch of tropical mountains in the Americas escape its scourge, the Darien National Park in Panama, and scientists are scrambling to save what species they can.

Frogs have been taking a beating over the last three decades, due in large part to a ruthless killer called chytrid fungus. Identified in the late ’90s, the fungus is startlingly lethal, driving 50% of species into extinction and killing 80% of individuals within five months of appearing at one location in Panama. It spreads through water via spores, affecting even areas where humans have not penetrated. “It is the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction,” wrote a team of scientists in a 2005 World Conservation Union report [pdf].

It’s no secret that an alarming number of species around the world, especially vertebrates, are in trouble. But is the notion that the Earth is on the brink of a sixth major extinction event—the first since the dinosaur die-off—true, or alarmist? In Nature this week, a team of scientists sought to answer the question directly by counting as many species (and extinctions) as they could in the fossil record and the recent historical record. The result is gloomy news: There’s still a chance to avert much of the crisis, but if nothing changes, such a mass extinction event really could happen in the span of just a few centuries.

Mass extinctions include events in which 75 percent of the species on Earth disappear within a geologically short time period, usually on the order of a few hundred thousand to a couple million years. It’s happened only five times before in the past 540 million years of multicellular life on Earth. (The last great extinction occurred 65 million years ago, when the dinosaurs were wiped out.) At current rates of extinction, the study found, Earth will enter its sixth mass extinction within the next 300 to 2,000 years. [MSNBC]

That range of time the researchers give is so large because of the great diversity of life—it makes it hard to track exactly how many species are disappearing, and how quickly. (Indeed, DISCOVER has covered how biologists are discovering many new species these days just as those species face extinction). So Anthony Barnosky and his team made conservative estimates based on the available evidence. For instance, they pegged the rate of mammal extinction at 80 species out of a total of 5,000-plus in the last five centuries. That may not sound like much, but when you consider the speed at which things typically happen on a geologic scale, it is a faster rate of species loss than the previous five mass extinctions saw, scientists believe.

The Permian extinction event was the biggest shake-up of life that Earth has ever seen: in the “Great Dying” that took place 250 million years ago, more than 90 percent of marine species were killed and about 70 percent of land animals vanished. The cause of this catastrophe has been debated for years, but new research suggests that volcanic eruptions triggered massive coal fires that pumped pollution into the air, eventually poisoning the planet.

The study, published in Nature Geoscience, is based on new findings from arctic rocks that date back to the Permian period, when all of the planet’s land masses formed a supercontinent called Pangaea. When the researchers analyzed the rocks, they found signs of a coal-based apocalypse.

Besides the usual miniscule clumps of organic matter, they also found tiny bubble-filled particles called cenospheres. These frothy little blobs form only when molten coal spews into the atmosphere, the researchers say…. [The cenospheres] must have been created when massive amounts of molten rock—more than 1 trillion metric tons—erupted through overlying coal deposits in Siberia to form lava deposits known as the Siberian Traps. [ScienceNOW]

This fossil of an ancient winged reptile, bought from a farmer in China’s Liaoning province, tells a dramatic tale. About 160 million years ago, a female pterosaur fractured its wing and sank to the bottom of a muddy lake. Somehow, in the process of either dying or decomposing, she expelled a single egg, which has been preserved through the ages.

That’s the story that researchers told in a study published in the journal Science, anyway. And if the remarkably preserved fossil of the reptile Darwinopterus is female, they say, it sheds light on the sex differences and mating rituals of the extinct species. The preserved egg also seems to reveal new details of pterosaur reproduction.

Pterosaurs were the first vertebrates to take to the air, first appearing in the fossil record some 220 million years ago in the late Triassic period. Before their demise 65 million years ago the group evolved to include the largest flying animals ever to live – some had a wingspan of 10 metres. [New Scientist]

The Internet has been burning up with an ice age storyline over the past few days: Researchers in Japan led by Akira Iritani announced their plan to clone a woolly mammoth within four to six years, recreating a colossal beast not seen on Earth in thousands of years. But as enthusiastic as DISCOVER is for cloned mammoths (and believe us, we’re psyched), the project is still a long way from success.

First, the backstory.

Researchers from Kinki University’s Graduate School of Biology-Oriented Science and Technology began the study in 1997. On three occasions, the team obtained mammoth skin and muscle tissue excavated in good condition from the permafrost in Siberia. However, most nuclei in the cells were damaged by ice crystals and were unusable. The plan to clone a mammoth was abandoned. [Daily Yamiuri]

That initial effort was a DISCOVER cover story back in 1999. Now, though, the dream is back, thanks to newly developed methods to get around that icy problem.

The team, which has invited a Russian mammoth researcher and two US elephant experts to join the project, has established a technique to extract DNA from frozen cells, previously an obstacle to cloning attempts because of the damage cells sustained in the freezing process. Another Japanese researcher, Teruhiko Wakayama of the Riken Centre for Developmental Biology, succeeded in 2008 in cloning a mouse from the cells of another that had been kept in temperatures similar to frozen ground for 16 years. [AFP]

About 540 million years ago, things were looking pretty rosy for complex life on Earth. Conditions were favorable, and the diversity of multicellular organisms took off during the so-called Cambrian Explosion. Trilobites frolicked. Brachiopods abounded. And then, things went south.

Between 490 million and 520 million years ago, a swift extinction event wiped out many of the Cambrian lifeforms. Geologists Benjamin Gill and Graham Shields-Zhou thinks they have found the trigger right in the midst of that era. According to their study in this week’s Nature, the ocean’s oxygen level plunged and the sulfur levels rose sharply 499 million years ago, killing off species that could not quickly adapt. That included some, but not all, of the trilobites that ruled the seas of the time.

Gill’s team decided to look at a specific subset of Cambrian extinctions that began 499 million years ago and lasted for 2 million to 4 million years. Other researchers had proposed that low oxygen levels — a condition known as anoxia — could be involved. But no one had marshaled enough evidence to prove that. [Science News]

The key to showing it in this case is in the chemical compositions of the samples the team collected, which hold clues to the ocean conditions of the time.

Gill and his colleagues took samples of 500-million-year-old rock from six locations around the world and measured the amounts of various isotopes of carbon and sulphur. Both were significantly different from the norm, suggesting that enormous amounts of carbon and sulphur were being buried. In modern oceans, this only occurs in low-oxygen waters like the Black Sea. [New Scientist]

The next question is, what drove down the oxygen levels so quickly? To that, Gill doesn’t have an answer. But such cyclical dramatic changes driving extinction is the rule, not the exception—there were several events during the latter Cambrian when many species were wiped out, and anoxia could have been at play in some of those, too.